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| Home > Publications database > Heiße Reaktionen in den Systemen $^{11}C/H_{2}O(l), ^{11}C/H_{2}O-NH_{3}(l)$ und $^{13}N/H_{2}O(g)$ |
| Home > Publications database > Heiße Reaktionen in den Systemen $^{11}C/H_{2}O(l), ^{11}C/H_{2}O-NH_{3}(l)$ und $^{13}N/H_{2}O(g)$ |
| Book/Report | FZJ-2018-02746 |
; ;
1987
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18392
Report No.: Juel-2119
Abstract: The chemical reactions of hot $^{11}$C with liquid water and a water ammonia mixture of mass ratio 3:1 and of $^{13}$N with water vapour were studied at T=295K. $^{11}$C was generated by the nuclear processes $^{16}$O(p,$\alpha$a pn)$^{11}$C and $^{14}$N(p,$\alpha$)$^{11}$C. $^{13}$N was produced via the $^{16}$O(p,$\alpha$) $^{13}$N nuclear reaction. The activations were carried out in the cyclotron JULIC of the Institut für Kernphysik und in the compact cyclotron CV 28 of the Institut für Festkörperforschung of the KFA. The proton radiation dose was varied from D* = 2.8 $\cdot$ 10$^{-3}$ to 0.28 eV per target molecule for the system $^{11}$C/H$_{2}$O(l), from D* = 2.2 to 32 eV for the system $^{11}$C/H$_{2}$O-NH$_{3}$(l) and from D* = 0.13 to 6.2 eV for the system $^{13}$N/H$_{2}$O(g), in order to follow radiolytic changes of the reaction products. The analysis of the $^{11}$C- and $^{13}$N-recoil products was done by radiogaschromatography on Porapak-Q and Poropak-T columns. Products of the system $^{11}$C/H$_{2}$O(l) were $^{11}$CO$_{2}$ (98-100 % radiochemical yield) and $^{11}$CO (max. 1.5 %). The plot of these yields versus radiation dose fits well with that of the results obtained earlier by Stenström for lower dosesranging from D* = 10$^{-6}$ to 4 $\cdot$ 10$%^{-3}$ eV. At medium and high doses the reactive OH and O$_{2}$H radicals are responsible for the oxidation of all carbon compounds to CO$_{2}$. For the system $^{11}$C/H$_{2}$O-NH$_{3}$(l) six products ($^{11}$CO$_{2}$, $^{11}$CO, H$^{11}$COOH, $^{11}$CH$_{2}$O, $^{11}$CH$_{3}$OH and $^{11}$CH$_{4}$) were observed at radiation doses up to D* = 32 eV. In pure water, the last four of the products are only stable at D* < 10$^{-4}$ eV. NH$_{3}$ acts as a donor of H-radicals which neutralize the OH radicals and, thus, protect the products from oxidation to $^{11}$CO$_{2}$. In the system $^{13}$N/H$_{2}$O(g) five products were detected: $^{13}$NO$_{2}$, $^{13}$NO, $^{13}$NN, $^{13}$NNO and some $^{13}$NH$_{3}$. The formation of $^{13}$NN and $^{13}$NNO is due to N$_{2}$ trace impurities in the water vapour. $^{13}$NO is the main product at lowest doses with radiochemical yields exceeding 45 %. With increasing radiolysis $^{13}$NO is changed to $^{13}$NO$_{2}$. At higher doses $^{13}$NN becomes the main product. These experiments close a gap in the hitherto available data an chemical effects of $^{11}$C and $^{13}$N nuclear recoil in H$_{2}$O. They enable a comparison of the reactions in the three aggregate states of H$_{2}$O. It can be demonstrated, that the product spectrum depends an concentration and mobility of the most important radicals H and OH ($O_{2}$H). The true hot, " primary" products observed at lowest doses in the gas phase are the simplest oxygen compounds. $^{11}$CO and $^{13}$NO. They are probably formed by a direct attack an the water molecule followed by elimination of two H. These reactions are of interest for chemical interactions of the solar wind with the H$_{2}$O vapour containing coma of comets. In the liquid and in particular in the solid state, the primary product spectrum consists of a multitude of carbon and nitrogen compounds of all oxidation states. The high variability of product formation is of interest for the abiotic build-up of organic compounds by hot collision reactions in extraterrestrial matter. The system $^{11}$C/H$_{2}$O-NH$_{3}$(l) seems to bear some importance for the production of labelled precursors for the synthesis of radiopharmaceuticals. The interesting products $^{11}$C/H$_{2}$O and $^{11}$CH$_{3}$OH are still formed under intensive irradiation which is necessary for the production of high radioactivities for nuclear medical application. For the solid system $^{11}$C/H$_{2}$O-NH$_{3}$ it follows from the comparison of effects in different aggregation states of H$_{2}$O, that it may tolerate even higher doses than the liquid system.
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